Manufacture of light-sensitive gelatinsil ver halide photographic layers



MANUFACTURE OF LIGHT-SENSITIVE GELATIN- SHJVER HALIDE PHOTOGRAPHIC LAYERS John L. Foster, Wealdstone, Harrow, England, assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application June 29, 1954, Serial No. 440,273

1 Claim. (Cl. 117-34) This invention relates to the preparation of photographic layers in which the silver halide is in high concentration in the lower layer thereof, the top layer being practically clear gelatin.

The preparation of silver halide emulsion layers of the Schumann type in which the emulsion layer divides itself into a lower layer containing most of the silver halide and the top layer of practically clear gelatin is described in British Patent No. 688,980. In the procedure described there a fluent gelatino silver halide emulsion is applied as a coating onto a support and while the emulsion layer is still fluid, sedimentation of the silver halide is effected by gravitational or centrifugal force until at least 70% of the silver halide therein has deposited in the lower portion of the gelatin layer, following which the emulsion coating is dried. A procedure of the nature of that described in that British patent requires manual operation rather than machine coating which involves the formation of plates containing the emulsion coating thereon, the maintaining of the coated plates in a horizontal position for several hours to allow sedimentation or the use of centrifuging to accomplish the same purpose and the drying of the layer so formed.

The present invention constitutes an improvement over the invention as claimed in British Patent No. 688,980 in that a silver halide emulsion layer is employed in which the relative proportions of water and gelatin are such that the emulsion will set at room temperature, is set directly after coating upon a support therefor and is subsequently made fluent by heating and the silver halide is allowed to settle under conditions which prevent the coating from drying until the desired sedimentation has occurred.

The procedure employed in accordance with the present invention allows the initial coating operation to be carried out at high speed followed by setting and if desired drying if the sedimentation operation need not be carried out simultaneously with or immediately subsequent to the coating step. The settling operation of the emulsion layer can be carried out at such time as is convenient with the operator and without any possibility of any distortion or movement of the emulsion layer relative to the paper or film base upon which the emulsion layer has been coated. By the present invention the emulsion layer is immediately set after coating in contrast to methods in which the settling procedure is carried out on the freshly coated photographic product.

In operating the settling procedure on emulsion layers which have been dried such as where storage has been carried out it is preferable to first soak the emulsion layer in water particularly distilled water so that such emulsion layer will readily become fluent when heat is applied thereto. The coating which has been converted to a liquid or semi-liquid form such as by warming to a temperature of 40 C. or above is prevented from drying by any convenient method such as for instance by maintainin nited States Patent 2|790"7 2i8 Patented Apr. 30, 1957 the atmosphere of the room or cabinet in which the settling operation is carried out at a very high relative humidity or by coating the fluent layer with a water impermeable lacquer. This operation can be conveniently carried out by subjecting the emulsion layer to an atmosphere of air having an elevated temperature and a high relative humidity such as of l00%.

The coating of the emulsion layer upon the support can be done by any of the normal methods such as by a machine coating operation whereby a very uniform coating is applied to the support. The sedimentation, it achieved by the action of the force of gravity, is best carried out while the coated plates are in a horizontal position either with the support side downwards or uppermost. After sedimentation the coatings may be dried by changing the condition of the circulating air. If desired, centrifuging may be employed for sedimenting the silver halide in the emulsion layer. Our invention is especially adapted for use in connection with coarse grain photographic emulsions whereby very rapid settling of the silver halide may be obtained when the emulsion layer is in a fluent condition. After sedimentation of the silver halide to the desired point, the emulsion coating may be dried by the use of air of lower relative humidity.

The following example illustrates my invention:

An X-ray silver halide emulsion containing 6% of gelatin and no hardening agent was coated on halfplates at a coating weight of grains of silver halide per 11 square ft., set, dried and packed. At a later date the plates were soaked in distilled water for 5 minutes at room temperature and were then placed-on level glass shelves in a cabinet wherein air was circulated at a temperature of 40 C. and 95-100% relative humidity over the plates for 1 hour, whereupon substantially complete sedimentation was obtained. The plates were then dried and were sensitized to ultraviolet light by washing away the gelatin with water at 40 C. There was no trace of any silver halide having been removed with the gelatin indicating that the sedimentation had been complete. The plates so produced appeared to have excellent sensitometric characteristics.

It is desirable in preparing photographic products in accordance with my invention that the emulsions employed be somewhat dilute such as having a gelatin concentration of from 5-20 grams of photographic emulsion per liter so as to facilitate the settling of the silver halide particles therein, this feature as well as other features which are favorable to the preparation of such products being taught in the prior art as, for example, in British patent No. 688,980. It is often desirable in'preparing photographic products as described to remove the uppermost layer consisting mostly of gelatin which overlies the sedimented layer while in other cases it is desirable to retain the overlayer of gelatin to act as a protective coating to the silver halide underlayer of the product prepared as described.

I claim:

A method of preparing a photographic product which comprises remelting by means of water and an elevated temperature a silver halide gelatin emulsion layer on a support, maintaining the layer in molten form and in horizontal position in an atmosphere having a relative humidity of approximately 95-100% until the desired settling of silver halide has occurred followed by drying the emulsion layer.

References Cited in the file of this patent UNITED STATES PATENTS 2,269,169 Van Derhoet et a1. Jan. 6, 1942 

